Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Simuliidae”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60Linked to original sources
PubMed1989

A community trial of ivermectin in the onchocerciasis focus of Asubende, Ghana. I. Effect on the microfilarial reservoir and the transmission of Onchocerca volvulus.

A community trial of the microfilaricide ivermectin was undertaken in an isolated focus of hyperendemic savanna onchocerciasis in Ghana. One of the objectives was to determine the effect of mass treatment on the microfilarial reservoir and on the transmission of Onchocerciasis volvulus. Since 1978 the focus has been under entomological surveillance. This was intensified from 1 September 1987 till 11 February 1988 with daily vector collection and dissection of over 30,000 flies. A total of 14,991 people were treated with ivermectin on 7-10 October 1987. Skin snip surveys were done pre-treatment, and at two and four months after treatment. The mean skin microfilarial load in treated persons had fallen by more than 96% two months after treatment. During the next two months there was an increase in microfilaria loads which appeared to be faster than reported in the clinical trials. The total reservoir of skin microfilariae available for transmission had been reduced by an estimated 68%-78% two months after treatment. This was consistent with the entomological results which indicated a reduction in transmission of 65%-85% during the first three post-treatment months. The present study has shown for the first time that mass chemotherapy can significantly reduce onchocerciasis transmission. However, the remaining level of transmission was still unacceptably high and further studies are required to predict the long term impact of repeated mass treatment.

Animals↗
PubMed1989

On the possibility of bovine Onchocerca species infecting Simulium damnosum s.l. in the forest zone of Sierra Leone. II. Biting densities and filarial infections in Simulium spp. and Culicoides spp.

Previous studies of bovine Onchocerca spp. in cattle in Sierra Leone indicated that only O. gutturosa was transmitted in the forest zone at high intensity. To determine its vector(s) and the extent to which Onchocerca-like infections in Simulium damnosum were likely to be of bovine origin, three lines of investigation were pursued. Firstly, a study was made of the biting flies attacking an ox bait animal over a 14-month period at Njala University Campus, near Bo. Secondly, attempts were made to infect the dominant local forest cytospecies of S. damnosum s.l. with O. gutturosa by feeding them on an infected ox under a bed-net. Thirdly, S. damnosum s.l. were infected by intra-thoracic injection of O. gutturosa microfilariae (mff). In 113 collections made at dawn and dusk at weekly intervals from the ox bait, 624 simuliids and 7740 Culicoides spp. were collected. Almost all the simuliids were S. damnosum s.l. which, on the basis of iso-enzyme examination and knowledge of local breeding sites, were identified as S. soubrense 'B'. Although this cytospecies fed readily on the ox at ventral sites where O. gutturosa mff occurred and the bed-net experiments showed that 16.1% of engorged S. soubrense 'B' ingested an average of 3.3 O. gutturosa mff each, no development occurred. The refractoriness of S. damnosum s.l. to O. gutturosa was confirmed by the intra-thoracic injection experiments. The predominant Culicoides spp. attacking the ox bait were C. krameri, C. trifasciellus and C. fulvithorax, with smaller numbers of C. schultzei. In 5803 dissected Culicoides spp., natural infections of Onchocerca-like larvae, presumed to be O. gutturosa, were found in 0.3% of C. fulvithorax, 0.1% of C. trifasciellus and 0.06% of C. krameri. It was concluded that, in the forest zone of Sierra Leone, S. damnosum s.l. is not a vector of O. gutturosa and all Onchocerca-like larvae in S. damnosum are likely to be O. volvulus, while the natural vectors of O. gutturosa are the Culicoides species C. fulvithorax, C. trifasciellus and C. krameri.

Animals↗
PubMed1989

Cytotaxonomy of Sirba form populations of the Simulium damnosum complex in west Africa: amendments to sex chromosomes and sibling status.

The banding pattern of larval salivary polytene chromosomes was analysed to re-examine the distribution, by sex and geography, of the sex linked inversion (IS-3) in "Sirba" form which was previously described as consisting of Simulium sirbanum and S. sudanense (Vajime and Dunbar, 1975). West African larval samples from seven countries within the Onchocerciasis Control Programme area and some adjacent locations were used. It was concluded that "Sirba" consists of two indisputable cytoforms, one distinguished by X0Y0 males and X0X0 females, the other by X1Y0 males and X1X1 females; and that the cytoforms are cytologically variable populations of a single cytospecies, S. sirbanum. It is argued that the species is in the process of incipient speciation.

Africa, Western↗
PubMed1989

The chemotherapy of onchocerciasis. XIII. Studies with ivermectin in onchocerciasis patients in northern Ghana, a region with long lasting vector control.

One hundred and ninety eight patients with moderate to heavy infections with Onchocerca volvulus were randomly assigned to receive single doses of 100, 150 or 200 mcg/kg of ivermectin or matching placebo capsules. Detailed systemic, ocular and parasitological examinations were carried out at intervals over a period of one year. Nodules were excised twelve months after treatment to evaluate the effect of the treatment with ivermectin in adult O. volvulus. The three ivermectin-treated groups produced massive reductions in skin microfilariae (over 97%) with low levels being maintained over one year. The 150 and 200 mcg/kg doses were however superior to the 100 mcg/kg dose in achieving a greater reduction in skin microfilarial counts initially and in maintaining significant lower levels throughout the period of observation. There was no difference between the 150 and 200 mcg/kg doses at anytime. The three ivermectin doses were equally effective in the clearance of ocular microfilariae. The proportion of dead adult worms was very high in all treatment groups, which is effected by the successful ten years lasting vector control in northern Ghana. In spite of this superannuation of the worm population, an impact of the treatment with ivermectin on the reproductivity of the parasite could be shown. Systemic total clinical reaction was mild and was similar in the ivermectin treated groups. However, severe symptomatic postural hypotension (SSPH) was limited to patients treated with 150 or 200 mcg/kg of ivermectin. Ocular reactions were mild in all patients and no ocular deficiency occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

A semi-automated system of intrathoracic injection for the large-scale production of Onchocerca lienalis infective larvae.

Intrathoracic injection of Onchocerca lienalis microfilariae (mf) into Simulium ornatum sl. is a highly efficient procedure for routine production of infective stage larvae (L3). This bovine parasite provides a useful analogue of Onchocerca volvulus from man, which presents far greater difficulties for L3 production outside endemic areas of onchocerciasis. Using novel systems for the infection and caging of adult blackflies in the laboratory, mean yields of 10.1-38.6 L3 per fly have been regularly obtained. Cyclical maintenance of either the parasite or vector is not a requirement for the success of this approach. An automated device has been developed to control deliveries of mf inoculations, that permits an experienced operator to perform injections at a rate of approximately 200 flies an hour. Mass recoveries of larvae by Baermann extraction appeared to be highly efficient, contrasting an earlier report on the application of this method to Onchocerca L3. Typical performance of these techniques in routine use over a period of time is illustrated with data on 18,000 inoculated blackflies, which yielded over 100,000 L3. Viability of the L3 obtained by the procedures described was confirmed by successful transmission of patent infections to laboratory-reared calves.

Animals↗
PubMed1987

Population dynamics of Onchocerca volvulus after 7 to 8 years of vector control in West Africa.

In an attempt to describe the changing population dynamics of Onchocerca volvulus during a period of vector control, nodulectomies were undertaken in 256 patients from ten villages in the Onchocerciasis Control Programme (OCP) and in 74 patients from two villages in an area with ongoing transmission. A total of 1198 nodules were excised and 4350 adult worms were isolated and examined for viability and productivity. In the OCP villages, the worm population is ageing and dying without replacement by new generations of parasites and various findings signal a breakdown of the worm population after about 12 years interruption of transmission. The sexual activity of the worms was significantly reduced. A Productivity Index was developed to measure the microfilariae production at the nodule level. The reduction in this index for the OCP villages correlates closely with the decline over the control period in the community microfilarial loads in the skin. The results show that it is not only the longevity of the parasite which will determine the duration of vector control, but that the reduced productivity of the ageing parasite population is of equal importance.

Africa, Western↗
PubMed1985

The story of Bacillus thuringiensis var. israelensis (B.t.i.).

The isolation and the characteristics of Bacillus thuringiensis var. israelensis is reviewed. Included in the review are full descriptions of the nomenclature, mosquito target range of this potent mosquitocidal bacterium, as well as the genetics and biochemistry of the toxins.

Animals↗
PubMed1988

The effect of tolypin in Tolypocladium niveum crude extract against mosquito and blackfly larvae in the laboratory.

The efficacy of tolypin against mosquito and blackfly larvae was studied under laboratory conditions. It was tested against Culex molestus, Aedes aegypti, Anopheles maculipennis, Simulium noelleri and Odagmia ornata. A concentration 0.1 mg/ml caused 100% mortality in all species tested and a concentration 0.001 mg/ml caused 100% mortality only in the two species of blackflies used within 24 hours.

Aedes↗
PubMedDate not supplied

[Systematics of black flies of the genus Phoretodagmia Rubzov].

A key for identification of species of the genus Phoretodagmia is given. Lectotype and paralectotypes of the species Ph. ephemerophila (Rubzov) are designated. The species name obicumbensis Rubzov is considered as a junior synonym of the species name ephemerophila (Rubzov).

Animals↗
PubMed1988

Anthropophily, zoophily and roles in onchocerciasis transmission of the Djodji form of Simulium sanctipauli and S. squamosum in a forest zone of Togo.

Adult female Simulium damnosum s.l. were caught at human and cattle bait at Djodji in Togo. Two members of the Simulium damnosum complex, the Djodji form of S. sanctipauli (74.9% of the total catch) and S. squamosum (25.1%), were identified and both were mainly anthropophilic. Although each species was also recorded feeding on cattle or turkey baits, most flies which were caught at animal baits did not take blood from them. Flies caught unfed at the cattle bait tended to be larger and have higher parous rates than those caught on man. S. sanctipauli flies were on average larger than S. squamosum but the sizes of both species varied seasonally. Infections with Onchocerca volvulus were found in both species. The infection rates varied seasonally with the highest levels occurring in the wet season. The Djodji form of S. sanctipauli is potentially a much more efficient vector (162 L3/1000 biting flies) than both S. squamosum (48 L3/1000 biting flies) and the S. sanctipauli s.l. found in the Cote d'Ivoire.

Animals↗
PubMed1988

The relationship between innate susceptibility to Onchocerca, and haemolymph attenuation of microfilarial motility in vitro using British and west African blackflies.

The effect of haemolymph from individual flies of differing species of Simulium were compared in their ability to attenuate Onchocerca microfilariae in vitro. Small maintenance systems, each of 3-4 microliters total volume, were set up in Terasaki plates. Three British species of greatly differing susceptibilities to Onchocerca lienalis (Simulium ornatum, S. equinum and S. vernum) were compared in their effect on O. lienalis. Three forms of the S. damnosum complex from Liberia (S. yahense and 2 geographical variants of S. soubrense) were similarly compared in their effects on O. volvulus microfilariae. The more refractory species in both sets of experiments were found to significantly reduce the in vitro motility of the microfilariae more than the susceptible species. It is proposed that this innate variation in in vitro attenuation, may be caused be humoral haemolymph proteins. Such an assay, perhaps in a modified form could be used in predicting vector susceptibility. It could also be used to analyse mechanisms responsible for variation in susceptibility, of different S. damnosum complex members, to the geographical forms of O. volvulus.

Africa, Western↗
PubMed1988

Simulium (Edwardsellum) rasyani n.sp., the Yemen species of the Simulium damnosum complex.

The examination of the polytene chromosomes of the Yemen representative of the Simulium damnosum complex revealed hitherto unknown arrangements distinct enough to justify the description of this form as the new species Simulium (Edwardsellum) rasyani. The newly recognized inversion II L-60.65 was always present and found to be homozygous in 62% and heterozygous in 38% of the 106 larvae which were examined. A short description is given of the morphology of the females, males, larvae and pupae. Populations from the five permanent Wadis Kabir, Rasyan, Al Barh, Zabid, and Surdud were genetically and morphologically very uniform.

Animals↗
PubMed1988

Low temperature storage and pupal survival in the Simulium damnosum complex.

Pupae of the Simulium damnosum complex were exposed for different time periods to temperatures of 0, 4, 8 and 12 degrees C before returning to ambient temperature (24-28 degrees C). As the period of exposure to the low temperatures increased, pupal survival decreased. A one day exposure even to 0 degrees C had little effect on survival, whereas for a 4 day exposure, the optimum survival occurred at 8 degrees C with a total of 46% emergence. Young pupae (pale cuticle) had greatest emergence after exposure to 12 degrees C, the old ones (dark sclerotised cuticle) after exposure to 8 degrees C. Exposure to the different cold temperatures did not significantly affect the longevity of the emerging adults. Low temperature storage of pupae is thus a viable method for long distance transportation of living specimens of blackflies.

Animals↗